Field
This application relates generally to wellbore surveying and, more particularly, to systems and methods for determining the position of a wellbore relative to underground formations for oil field and gas field exploration and development.
Description of the Related Art
A survey tool configured to be used in a wellbore can comprise one or more sensors that are configured to provide information indicative of a position, orientation, or both of the survey tool relative to the Earth. For example, the survey tool can comprise at least one accelerometer sensor configured to provide at least one data signal indicative of the orientation of the survey tool relative to the center of the Earth. For another example, the survey tool can comprise at least one magnetic sensor configured to provide at least one data signal indicative of the orientation of the survey tool relative to the magnetic field of the Earth. For still another example, the survey tool can comprise at least one gyroscopic sensor configured to provide at least one data signal indicative of the orientation of the survey tool relative to the rotation axis of the Earth. The at least one gyroscopic sensor can comprise a rate gyroscope (e.g., a spinning gyroscope, typically with the spin axis substantially parallel to the wellbore) which undergoes precession as a consequence of the Earth's rotation and which can detect the components of this precession and generate information indicative of the orientation of the rate gyroscope's spin axis relative to the Earth's axis of rotation (e.g., information indicative to the orientation of the survey tool relative to true north).
As a wellbore is drilled in accordance with the well plan, further geological data can be collected using logging sensors, e.g., which provide measurements of gamma ray radiation or formation resistivity. These data are used to update knowledge of the geological formation and adjust the wellbore trajectory via a process known as geo-steering. This process can be applied to enable a desired geological target to be reached or to ensure that the wellbore remains within a desired hydro-carbon-bearing rock formation.